With the discovery that many cDNA copies of picornaviral RNA genomes result in the synthesis of infectious virus after transfection into mammalian cells, picornaviruses became amenable to genetic manipulations. Because picornaviruses interact extensively with host macromolecular pathways, these viruses have been used as tools to study the mechanisms of host cell translation, transcription and protein secretion. The overall aim of this proposal is to study specific viral- host interactions that occur in infected cells, with the ultimate goal to understand picornavirus-induced pathogenesis. The first aim was prompted by the knowledge that picornaviral mRNAs are translated by a novel internal initiation mechanism. Because the host cell translation apparatus can support this translational initiation mechanism in uninfected cells, we postulate that many host cell mRNAs use this unusual initiation mechanism. To identify them systematically, a sensitive differential RNA display method will be employed to detect cellular mRNAs that are associated with polysomes in poliovirus infected cells at a time when host cell translation is inhibited. Various forms of the translation initiation factor eIF-4G have been implicated to be important in translation initiation by both the conventional 5 plus end- dependent scanning mechanism and the internal initiation mechanism. In the second aim, the roles of the various forms of eIF-4G in host cell translation and the poliovirus infectious cycle will be studied in cells in which the normal eIF-4G gene is inactivated. In a third aim, the outcome of the relocalization of nucleolin from the nucleolus to the cytoplasm on viral gene expression will be studied in cell-free extracts. In addition, a virus-encoded function that induces the relocalization of nucleolin will be sought by monitoring the intracellular localization of nucleolin in the presence of individual viral polypeptides. In the last aim, genes will be identified that confer susceptibility to picornavirus infections. Random host genes will be disrupted by retroviral insertions and inactivated by expression of antisense RNA. Cells that have functionally inactivated allelic loci and that are resistant to infection by either poliovirus or rhinovirus will be selected and the disrupted genes will be identified.